1. Field of the Invention
This invention relates to catalysis. In one aspect, the invention relates to novel catalytic compositions of phosphorus, molybdenum, tellurium, copper and/or vanadium and an alkali metal while in another aspect, the invention relates to a process employing these catalysts for the oxidation of methacrolein to methacrylic acid.
2. Description of the Prior Art
The art is replete with various phosphomolybdic acid catalysts useful for the oxidation of acrolein to acrylic acid. See for example U.S. Pat. Nos. 4,101,448, 4,115,441, 4,042,533 and 4,166,190. However, not only do many of these catalysts contain tungsten but most are not suitable, at least from a commercial perspective, for the oxidation of methacrolein to methacrylic acid. Of those catalysts that are suitable from a commercial perspective, none are entirely so. All are subject to improvement in methacrylic acid selectively and thermal stability. Examples of catalysts now taught to be suitable for methacrolein oxidation are those of Belgian Pat. No. 823,897, British Pat. No. 1,482,686, U.S. Pat. Nos. 3,976,688 and 4,017,423. The Belgium patent teaches a phosphomolybdic acid catalyst that can be combined with any number of optional components; the British patent teaches a P-Mo-Cu-V-W catalyst that also can be combined with optional components, U.S. Pat. No. 3,976,688 teaches a catalyst similar to the phosphomolybdic acid catalyst of the Belgium patent but containing Rb, Cs or K; and U.S. Pat. No. 4,017,423 teaches a promoted Rb-Mo-P catalyst.
Japanese Pat. No. 2,051,316 teaches the oxidation of methacrolein to methacrylic acid over a catalyst of Mo-P-M-Te where M is K, Rb, Cs and/or Tl. British Pat. No. 1,478,828 and Netherlands Pat. No. 7602-438 teach a similar oxidation over a catalyst of Mo-P-M-As-Cu/V-Promoter where M is Li, Na, K, Rb and/or Cs and the promoter can be among others, Te.